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OIL PAINT

 

Any oil paint is a mixture of drying oil with pigments, i.e., coloring substances. How to prepare yourself, you will learn next, and now will base oil paint - drying oil.

Of course, drying oil (as well as some pigments) you can buy in the store. But for the young chemist this solution would be too boring. If you want to experiment, you need the oil to cook. However, it is first necessary to understand what it represents.

Natural drying oil prepared with vegetable oils. These oils have many; some of them are able to air dry (flax, hemp). Other dry only partially, and therefore called semidrying (for example, sunflower oil). And some oils are not dry at all - olive from olive, castor from castor.

But what does the word "dry" in relation to the oils? They contain no solvent, and dry like nothing. The way it is. Drying - term though well-established, but not quite accurate. Actually oil polymerized, their molecules are bound together, forming a solid insoluble and infusible polymer. But for this you need a substance that stitched together the relatively small molecules of oil. This substance o-oxygen. This is why the film of oil paint applied to the product, dries quickly. And the oil left in the Bank, only thickens from the surface: it is in contact with air.

But even drying oils themselves react with oxygen very slowly, and we had to wait very long until the paint is no longer dirty. However, this reaction can be accelerated considerably if you add a little oil catalyst. Those catalysts which accelerate the drying of the oil film, called the driers. Conventional drying oil is a mixture of oil (more recently increasingly synthetic) with a desiccant.

So, to prepare a varnish, it is necessary to mix a drying oil with a desiccant. You can also buy in the store, but isn't it better to prepare desiccant independently and experience to verify its validity?

Many dryers are the salt of organic acids. You can prepare this salt, enough known - processed resinat; resinate called salt of the acid included in the composition of rosin.

In porcelain (and if it's not metal) heat about 50 g of rosin. The temperature should be about 220-250°C. Rosin at a temperature melts. In this melt small portions while stirring type (carefully, not touching hands) 5 g of quicklime Cao. The reaction will produce resinate calcium.

If instead of lime to take 15 grams of litharge (lead oxide РbО), pounded to a paste with linseed oil, and add it in small portions, there is formed another desiccant - resinat lead. Litharge can be obtained from powder mixed with sodium or potassium nitrate (this is a common fertilizer). When heated mixture is formed of lead oxide РbО yellow, so that the reaction can be judged by the colour change. When it becomes sufficiently intense, stop heating, cool the mixture and treat it with water. Soluble reaction products go into solution, and with shaking light litharge separated from the heavy lead, unreacted, it will settle to the bottom. Thus, it is necessary to drain roiled opaque liquid with precipitate, filtered and dried - litharge ready.

The mixture of rosin with Cao or РbО should be heated until then, until you get a homogeneous mass. It drops place from time to time to clean the glass, and as soon as the drop will be transparent, heating can be discontinued.

Another very common desiccant - manganese oxide Mno2. It can be simple. Prepare two solutions of sodium sulfite Na2SO3and potassium permanganate KMPO4 (potassium permanganate). When you mix these solutions, the precipitate black powder. This is the desired oxide. Filter it and dry in the air without heating.

Whatever desiccant you have made, further steps will be the same. Add desiccant heated to 150-200°C flax or hemp oil - both drying. Experience manage better if the oil is refined. To 100 parts of the oil take 3-5 parts of the desiccant and stir until it dissolves. You have prepared a drying oil. Let it cool and check the action of the desiccant.

Apply the varnish in a thin layer on glass or metal, next apply the same film of pure oil, without catalyst. You can easily discover how desiccant accelerates drying oil. If you put some driers, compare their activity.

To get oil paint, linseed oil should be mixed with a pigment, prepared or improvised. Keep in mind that the pigment must be dried properly, pounded and sifted through the fine sieve, what you can find, or through cheesecloth, folded in half.

Such a fine powder, add dropwise a drying oil, each time stirring and rubbing it until you have a thick homogeneous mass, resembling porridge. RUB it carefully again and dilute all the same varnish, so she took the thick conventional masonry paints. Maybe your paint will be transparent, and it is not always desirable. To avoid transparency (as experts say that the paint was opaque), add to the oil with some white pigment. It will not affect the final color of the paint, but will deprive its transparency.

Even if you all are done carefully, the resulting oil-based paint will still be, perhaps, a little bit worse than from the store. But - with their hands.

O. Holguín. "Experiments without explosions"
M., "Chemistry", 1986

 

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